Method of operating a combustion apparatus

ABSTRACT

A method of operating a combustion apparatus such as an internal combustion engine is described, in which the apparatus includes at least one combustion chamber with an inlet port for primary combustion air, an apparatus to introduce into the combustion chamber primary fuel for combustion with the primary air, an exhaust port for combustion products, and an exhaust system for exhausting the combustion products to atmosphere, the method including introducing into the exhaust system secondary air, mechanically acting upon the secondary air and products of combustion in the exhaust system in the presence of a catalyst, to produce a reformed fuel, introducing the reformed fuel into the combustion chamber for combustion with primary fuel and primary air.

DESCRIPTION OF THE INVENTION

This invention relates to a method of operating a combustion apparatusand more particularly but not exclusively an internal combustion enginee.g. for a vehicle. Such an engine typically includes at least onecombustion chamber with an inlet port for primary combustion air, meansto introduce into the combustion chamber primary fuel for combustionwith the primary air, an outlet port for combustion products, and anexhaust system for exhausting the combustion products to atmosphere. Theprimary fuel may be petrol, diesel, liquid petroleum gas, for example,or any other suitable fuel or mixture of such fuels.

The development of internal combustion engines has tended to focus onmaximising the power output of the engine, achieving economy of fueluse, and the reduction of harmful emissions.

Particularly in the case of achieving reduction of harmful emissions,development has tended to concentrate on improving combustion within theengine for example by developing fuel injection systems which providefor improved fuel/air mixing in combustion chambers of the engine, andthen cleaning combustion products, for example by passing the combustionproducts through catalytic converters for example.

The provision of catalytic converters is problematic because suchdevices only tend to operate to their maximum performance once very hot,such that during short journeys for example in which engines may notattain an optimum operating temperature, such catalytic convertersprovide substantially no beneficial effect. Moreover, such convertersare expensive and require frequent replacement, as they are easilycontaminated.

In previous patent application EP-A-0744006 there is proposed anapparatus for improving combustion, by introducing into the combustionchamber of the engine, a vaporised secondary hydrocarbon based highcalorific value fuel, obtained by heating a mineral oil. Thus theefficiency with which the primary fuel is burned in the engine isenhanced, and this has the effect of reducing the production of harmfulexhaust emissions.

In previous patent application EP-A-041831 there is described an exhaustaspirator which is adapted to permit the introduction of relativelyclean air into an exhaust manifold of the engine to promote moreeffective exhaust gas discharge and to cause aspirated air to be drawninto a combustion chamber of the engine through an exhaust port thereof,rather than exhaust gases, during cyclic pressure changes which occur innormal engine operation.

According to a first aspect of the invention we provide a method ofoperating a combustion apparatus which includes at least one combustionchamber with an inlet port for primary combustion air, means tointroduce into the combustion chamber primary fuel for combustion withthe primary air, an exhaust port for combustion products, and an exhaustsystem for exhausting the combustion products to atmosphere, the methodincluding introducing into the exhaust system secondary air,mechanically acting upon the secondary air and products of combustion inthe exhaust system in the presence of a catalyst, to produce a reformedfuel, introducing the reformed fuel into the combustion chamber forcombustion with primary fuel and primary air.

Preferably, the reformed fuel is introduced into the combustion chambervia the exhaust port, e.g. soon after production, but it is envisagedthat the reformed fuel may be collected and stored, for later use, andmay be fed with the primary fuel into the combustion chamber.

It has been found that by utilising the method of the invention, asubstantial improvement in combustion efficiency can be achieved,resulting in much cleaner exhaust emissions and a significantimprovement in power output. Also whereas with previous proposals forimproved e.g. engine designs, it has been necessary to compromisebetween fuel efficiency and power output, utilising the presentinvention, such compromise is unnecessary.

Where the invention is applied to an engine, the method may includeintroducing the secondary air into the exhaust system via an exhaustaspirator e.g. similar to that disclosed in EP-A-0041831, which drawsair into the exhaust system during low pressure or partial vacuumconditions occurring during the cycle of pressure changes which occur inthe exhaust system during normal operation of the engine. Howeverwhereas in EP-A-0041831, the primary function of the aspirator is todamp down vacuum waves occurring in the exhaust system to improve theefficiency of exhaust gas discharge, in the method of the invention theexhaust aspirator is tuned to draw air into the exhaust system andmechanically to act upon the secondary air and products of combustion bymeans of pressure pulses, in a manner to optimise reformed fuelproduction.

Typically, an aspirator means suitable for the purpose of the method ofthe invention, includes a valve with a spring biased valve member, theforce of the spring acting to urge the valve member into engagement witha valve seat to close the valve, and the force of the spring beingovercome when sufficiently low pressure is developed in the exhaustsystem, to allow the secondary air to be drawn in through the valve.Tuning of such an aspirator means for the performance of the inventionmay involve adjusting the spring pressure so that the valve responds toa desired low pressure or partial vacuum at an appropriate time duringthe engine cycle, and in a manner to produce strong pressure pulses inthe exhaust system adequate mechanically to act upon the combustionproducts and secondary air present in the exhaust system to producereformed fuel.

It will be appreciated that in the case of an engine having a singlecombustion chamber, the spring may be adjusted to open the valve andallow the secondary air to be drawn into the exhaust system atcommencement of the piston's induction stroke, when a low pressure isdeveloped in the exhaust system as a result of the (single) pistonmoving in the combustion chamber to induce air therein through an airinlet port, prior to the exhaust port being completely closed by anexhaust outlet valve or the piston. In a multi-combustion chamberengine, where each piston will be in a different stroke position, thevalve may respond to low pressure developed in the exhaust system whenone or all of the pistons are at other stroke positions.

It will be appreciated that reference in this specification to primaryair being induced into the or each combustion chambers includes airbeing introduced into the combustion chamber or chambers by e.g. turboor other primary air introduction means.

The aspirator may be tuned to produce from the secondary air andcombustion products, which typically include un-burnt hydrocarbons,nitrous oxide gases (commonly known as “NOx”), carbon dioxide, carbonmonoxide and water (usually in the form of steam), reformed fuelincluding one or both of methanol and hydrogen gas, both of which maysatisfactorily provide a supplementary fuel. By operating an engine inaccordance with the invention, the amount of un-burnt hydrocarbons, NOxand carbon monoxide in the exhaust gases eventually emitted from theexhaust system to atmosphere has been found to be greatly reduced, andthe amount of carbon dioxide produced is significantly reduced

Preferably, the catalyst is provided by materials from which theaspirator is at least partly made, such as for example copper, but ifdesired Cerium may be provided in the vicinity of the aspirator which isparticularly good at enhancing secondary fuel production.

Where the apparatus is an engine, the reformed fuel may be introducedinto the or each combustion chamber of the engine as a result of apartial vacuum being established at the exhaust port at the end of anexhaust stroke of a piston thereof as the piston commences its nextinduction stroke, before the exhaust port is completely closed by anexhaust outlet valve or the piston.

Thus the reformed fuel will combust in the combustion chambersimultaneously with the primary air and primary fuel induced or injectedinto the engine during the next induction phase.

Where the combustion apparatus has a plurality of combustion chamberseach having an exhaust port, the exhaust ports may each open to anexhaust manifold, where the aspirator or other means for introducingsecondary air into the exhaust system may be located.

The method of the invention may include introducing reformed fuelobtained by mechanically acting upon drawn in secondary air and productsof combustion in the exhaust system, into an inlet manifold from whereair is introduced into the combustion chamber for combustion with theprimary fuel.

This may be achieved by allowing reformed fuel introduced into thecombustion chamber via the exhaust port while the exhaust port and inletports are both not fully closed, to pass out of the combustion chamberinto the inlet manifold for mixing with the air or air/fuel mixture inthe inlet manifold, for subsequent introduction into the combustionchamber together with primary and, and induced or injected primary fuel.

In addition to operating the apparatus in accordance with the primaryaspect of the invention described above, the method of the invention mayadditionally include introducing into the combustion chamber of theapparatus, a vaporised secondary hydrocarbon based high calorific valuefuel, obtained by heating a mineral oil, for example using an apparatusthe subject of EP-A-0744006.

A typical mineral oil may for example conform to British Standard 245.

The mineral oil may be heated electrically and/or by heat exchange withhot exhaust gases produced by the engine.

It has been found that by introducing into the engine or othercombustion apparatus a vaporised secondary hydrocarbon based highcalorific value fuel to be burnt with the primary fuel and primary air,the engine may be operated at a lower temperature than otherwise, and asa result, the amount of particularly NOx produced during combustion, isminimised.

The combustion apparatus may be an internal combustion engine e.g. anengine in which combustion of fuel in the combustion chamber isinitiated by spark, or a Diesel cycle engine in which combustion isinitiated by heat caused by the compression of gases in the combustionchamber, or a spark assisted Diesel engine.

In the case of a spark ignition engine the primary fuel may be inducedand/or injected into the combustion chamber together with the vaporisedsecondary hydrocarbon based high calorific value fuel, although wherethe primary fuel is introduced by injection, the vaporised secondaryhydrocarbon based high calorific value fuel may be introduced with theinduced air.

In each case performance of the invention has been found to improve thepower output of the engine, to achieve improved economy of fuel use, andthe reduction of harmful emissions.

According to a second aspect of the invention we provide a method ofadapting a combustion apparatus having at least one combustion chamber,for operation in accordance with the first aspect of the invention, themethod including providing the combustion apparatus with means tointroduce into the exhaust system secondary air, providing meansmechanically to act upon the secondary air and products of combustion inthe exhaust system in the presence of a catalyst, to produce a reformedfuel, and means to introduce the secondary fuel into the combustionchamber of the apparatus via the exhaust port for combustion withprimary fuel and primary air.

Thus the invention readily lends itself to retrofitting to an engine,whereas conventional catalytic converters for example are provided tocleanse exhaust emissions have to be provided as original equipment e.g.by a vehicle manufacturer to ensure that there is space provided toaccommodate the converter and to ensure that the converter and engineoperate satisfactorily together. However a vehicle may be adapted toperform the invention during manufacture as desired.

Where the engine to be adapted to perform the invention includes acatalytic converter already, depending on the kind of engine controlemployed, steps may need to be taken to ensure satisfactory operation ofthe engine. For example where the engine control is so called“open-loop”, i.e. an engine management system of the vehicle is operatedsubstantially independently of the performance of the catalyticconverter, the method of the second aspect of the invention may beperformed without any additional steps being required. However where theengine control is so called “closed-loop” in that an input to the enginemanagement system is provided from a sensor associated with thecatalytic converter, the method may include disabling the sensor of thecatalytic converter or re-programming the engine management system sothat performance of the method of the first aspect of the invention doesnot detrimentally affect the performance of the engine managementsystem.

It will be appreciated that catalytic converters operate mostsatisfactorily with a rich fuel/air mixture being burnt in the engine.With a so called “closed-loop” engine management system, the sensorassociated with the catalytic converter senses the amount of un-burntfuel and carbon monoxide, in the combustion products, and the enginemanagement system sets the richness of the primary fuel/air mixture foroptimum performance of the catalytic converter. Because utilising thepresent invention un-burnt hydrocarbons and carbon monoxide are used upin providing reformed fuel, an un-modified closed-loop engine managementsystem would respond to the sensor unduly to increase the richness ofthe primary fuel/air mixture.

The invention will now be described with reference to the accompanyingdrawings in which:

FIG. 1 is a schematic illustration of an engine being operated inaccordance with the first and second aspects of the invention;

FIG. 2 is an illustrative partly exploded side sectional view of anexhaust aspirator for use in the method of the invention;

FIG. 3 is an illustrative side sectional view of a secondary fuelapparatus for use in the method of the invention.

Referring to FIG. 1, an engine 10 has at least one combustion chamber11. In this example the engine 10 is of the reciprocating type, in whichthe combustion chamber 11 is a cylinder in which a piston 12reciprocates. The invention is however applicable to other kinds ofinternal combustion engines such as for example rotary engines.

The or each combustion chamber 11 has an inlet port 15 through which, inthis example, primary combustion air is introduced, either by simpleinduction due to piston 12 movement, or with turbo assistance, and anexhaust outlet port 16. Both the inlet and outlet ports 15, 16 in thisexample are opened and closed by the operation of respective valves 17,18 which typically are controlled to open and close in accordance withthe engine cycle, e.g. by operating rods driven from a camshaft.

In this example, the engine is a Diesel engine in which primary fuel forcombustion is injected into the engine by an injector 19, and is ignitedas a result of heat generated as air is compressed in the cylinder. Inanother example, ignition of the primary fuel may be achieved with sparkassistance, and particularly in the case of a petrol spark ignitionengine, primary fuel may be introduced into the combustion chamber 11along with the primary air.

The primary air may be introduced into the combustion chamber from aninlet manifold 20. Of course where the engine 10 has a plurality ofcombustion chambers 11, the inlet ports 15 for each may be connected tothe inlet manifold 20. Air is provided to the inlet manifold 20 from anair inlet 21, via air filters etc. as is well known in the art, and/orthe air may be provided via a turbo device or otherwise.

The or each exhaust outlet port 16 is connected to an exhaust manifold23 of an exhaust system 24. Again in the case of a multi-combustionchamber 11 engine, the outlet ports 16 for each combustion chamber 11may be connected to the exhaust manifold 23. Combustion gases pass,possibly via a catalytic converter 25, from the exhaust manifold, toatmosphere.

In accordance with the invention there is provided a means forintroducing secondary air into the exhaust system 24, and in the presentcase, this is an aspirator device 26 which is described in more detailbelow with reference to FIG. 2, the aspirator 26 being adapted also toprovide for exhaust gases and introduced secondary air in the exhaustsystem 24, mechanically to be acted upon such that the exhaust gases andsecondary air provide a reformed fuel. The reformed fuel is then fedback into the combustion chamber 11 as hereinafter explained, and issubsequently burnt in the combustion chamber 11 along with primary fuel.

It will be appreciated that immediately subsequent to the piston 12performing an exhaust stroke in the combustion chamber 11, i.e. movingupwardly as seen in the drawings whilst the exhaust outlet port 16 isopen, and the piston 12 moves downwardly again to enable at leastprimary air to be introduced into the combustion chamber 11 with theinlet port 15 open, there will be a short but finite period in whichboth the inlet 15 and outlet 16 ports will simultaneously be open.During that period, a reduced pressure, or partial vacuum will beestablished at the outlet port 16 and as a consequence, gases from theexhaust system 24 will be drawn into the combustion chamber 11 alongwith the primary air from the inlet 15 port. Thus where the exhaustgases include reformed fuel, the reformed fuel will be introduced intothe combustion chamber 11.

Moreover, a very small amount of the reformed fuel may pass through thecombustion chamber 11 to the inlet port 15, and notwithstanding flowwill be predominantly in an opposite direction, a very small amount ofthe reformed fuel may pass to the inlet manifold 20 for mixing withprimary air. Thus the primary air subsequently introduced into thecombustion chamber 11 may contain a very small proportion of reformedfuel.

Moreover, in FIG. 1 there is shown an apparatus 30 by means of which asecondary high calorific value vaporised fuel may be introduced into theinlet manifold 20, for introduction with the primary air into thecombustion chamber.

Referring now to FIG. 2, an aspirator 26 suitable for allowing secondaryair to be introduced into the exhaust system 24 is shown. The aspirator26 is tuned to maximise reformed fuel production from the secondary airand combustion products.

The aspirator 26 includes a tube 32 which may be provided at one end 33,i.e. the lower end indicated in FIG. 2, with a male threaded boss, toenable the aspirator 26 conveniently to be attached to the outletmanifold 23, but the manifold 23 and aspirator 26 may otherwise bearranged to be connected.

The tube is preferably made of a catalytic material, such as copper,which promotes reformed fuel production, and if desired, Cerium oranother higher value but more efficient catalytic material, may bepresent in the exhaust system 24 further to promote the production ofreformed fuel.

At an opposite end 34 of the tube 32, at the top as shown in FIG. 2,there is provided a valve 35. The valve 35 includes a valve seat 36accommodated in a housing 37 which is in the form of a mushroom shapedcap in this example. A valve member, which in this case is a ball 40, isurged by a spring 41 into engagement with the valve seat 36 which isshaped to receive the ball 40, normally to close the valve and preventair passing the valve 35 into the tube 32. However the spring 41 isweak, and in the event that a low pressure or partial vacuum isexperienced within the tube 32, the force of the spring 41 will beovercome and the ball 40 will be removed from the valve seat 36 so thatair may be drawn in through the valve 35, and hence to tube 32 and theexhaust system 24.

The aspirator 26 may be tuned to maximise reformed fuel production bysetting the spring 41 pressure so that the valve 35 opens to maximisesecondary air inflow at appropriate points in the engine cycle.Moreover, the spring 41 and valve 35 construction generally are adaptedso that the secondary air is introduced as strong pulses, with the valveopening and closing sharply. The pulses thus produced, mechanically actupon the combustion products and secondary air in the exhaust system 24in the presence of the catalytic material, to reform fuel, typicallyhydrogen gas and methanol, which are introduced as described above intothe combustion chamber 11.

Other aspirator 26 constructions are no doubt possible. For example thevalve 35 construction may incorporate other than a ball shaped valvemember 40, e.g. a disc shaped valve member, with the valve seat 36 beingappropriately configured so that the aspirator 26 is tuned to maximisereformed fuel production. In FIG. 1, the tube 32 is shown to be bent,whereas in FIG. 2, the tube 32 is straight. The tube 32 may be bent asdesired to fit within an engine compartment of a vehicle.

In a practical embodiment, typically, the tube is about thirtycentimeters in length, and typically the valve 35 is about 5 cm inlength. The tube 32 diameter is typically about 0.79 cm.

The operation of the aspirator 16 has been described with reference toparticularly a single combustion chamber 11 engine 10, in which the lowpressure or partial vacuum necessary to cause the valve 35 to open toallow secondary air to be drawn into the exhaust system 24, occurs whenthe piston 12 is at or substantially at the top of its stroke with theinlet 15 and exhaust ports 16 open. It will be appreciated that in amulti-combustion chamber 11 engine 10, in which all of the pistons 12will be at different positions in their cycles at any one time, in orderto balance the engine 10, the valve 35 of the aspirator 26 may bearranged to open at a time which may not coincide with the piston 12 ofany combustion chamber 11 being at the top of its stroke with the inlet15 and exhaust ports 16 open. In a multi-combustion chamber 11 engine10, the pressure in the exhaust system 24 will tend to change accordingto a complex pattern. Nevertheless, the valve 35 of the aspirator 26 maybe arranged to open against the force of spring 41 when a set lowpressure or partial vacuum is experienced in the exhaust system 24. Thussecondary air/reformed fuel may dwell in the exhaust system 24 but beintroduced into the combustion chambers 11 when next a respective piston12 is at the top of its stroke with the inlet 15 and exhaust ports 16open. Thus the low pressure or partial vacuum required for theintroduction of secondary air into the exhaust system 24 may notcoincide with the low pressure or partial vacuum experienced locally ofthe exhaust outlet ports 16 of the combustion chambers 11 necessary forthe reformed fuel to be introduced into the combustion chambers 11.

Referring now to FIG. 3, there is shown an example of an apparatus 30 bymeans of which a secondary hydrocarbon based high calorific valuevaporised fuel may be introduced into the combustion chamber 11 (orchamber) along with primary air for combustion.

The apparatus 30 includes a reservoir 50 in which there is provided ahydrocarbon based liquid fuel, which conforms to British Standard 245.The container 50 may be filled with liquid fuel via a filler cap 51, anda dipstick 52 may be provided so that the liquid fuel level within thecontainer 50 may readily be determined.

Mounted in the reservoir 50, is an elongate inwardly extendingelectrical heater element 55, which is mounted via a threaded boss 56.The boss 56 is in threaded and sealing engagement with the container 50,or at least of a bottom wall 57 thereof in this example, and alsoprovides a mounting 58 for a sub-assembly 59. The sub-assembly 59includes a cylindrical housing 60 in which there is provided a coiledtube 61 which opens through the housing 60 at one end 62 thereof, into aspace 65 above the level of the liquid fuel in the container 50, and ata lower end 64, opens through the housing 60 below the liquid fuellevel.

When the electrical element 55 is actuated, by passing an electricalcurrent therethrough, liquid fuel in the coiled tube 61 is heated andvaporised. The vaporised fuel passes into the space 65 above the liquidfuel level, and hence through an outlet 66 to the inlet manifold 20 ofthe engine 10. Thus the vaporised fuel passes with the primary air, intothe combustion chamber 11.

Around the coiled tube 61 in the housing 60, there is insulation 63 sothat only the liquid fuel in the coiled tube 61 becomes heated. Moreoverbecause the coiled tube 61 is necessarily of small diameter and thusliable to blockage, the sub-assembly 59 is removable form the container50 by unscrewing from the mounting 58. To seal the sub-assembly 59 withrespect to the container 50, the sub-assembly may in use, be also inthreaded engagement with the container via a secondary mounting 68, andmay include some means, such as a knurled ring 70, to facilitate removaland insertion of the sub-assembly 59 in the container 50.

In another construction of secondary fuel apparatus 50, instead of anelectrical heater 55, or in addition thereto, means may be provided toenable the liquid fuel to be heated towards vaporisation, by anotherheat source, such as for example, hot exhaust gases produced by theengine 10.

It will be appreciated that an existing engine 10 may be adapted toperform the invention by providing an aspirator 26 tuned to reformedfuel production, in the exhaust manifold 23, and if desired by providinga secondary fuel providing apparatus such as apparatus 50 described towork in conjunction therewith.

Where the exhaust system 24 includes a catalytic converter 25, dependingon whether this is a passive or active device, when adapting a enginefor performance of the present invention, additional steps may need tobe performed.

For example, where the catalytic converter 25 includes a sensor 80 whichprovides an input to an engine management system 81, indicative of theconcentration of un-burnt hydrocarbons and carbon monoxide in theexhaust gases, the engine management system conventionally responds bysetting the richness of the primary fuel/air mixture to a level wherethe catalytic converter 25 can operate most efficiently. Where theinvention is performed, and the level of un-burnt hydrocarbons andcarbon monoxide in the exhaust gases are reduced by the method, thesensor 80 needs to be disabled and/or the engine management system 81re-programmed to ensure that the richness of the primary fuel/airmixture is not unduly increased.

In an engine in which for example the secondary fuel apparatus 50 isonly operated at intervals, the sensor 80 may be used, or another sensorprovided, to provide an input to the engine management system 81 inresponse to particular engine conditions arising to cause the secondaryfuel apparatus 50 to operate or not to operate, e.g. by switching theelectrical heating element 55 or other heating means on or off.

Various modifications may be made to the apparatus described whilstenabling the methods of the invention to be performed.

For example, in the example described, reformed secondary fuel isintroduced into the combination chamber via the exhaust port, forcombustion with the primary fuel. Particularly where an excess ofreformed fuel is produced, this may be collected and stored, andintroduced into the combustion chamber later, e.g. along with theprimary fuel rather than via the exhaust port.

The invention is not exclusively applicable to internal combustionengines, but may be applied to other combustion apparatus such as aboiler or furnace having a combustion chamber preferably with an exhaustport through which reformed fuel may be introduced

What is claimed is:
 1. A method of operating a combustion apparatuswhich includes at least one combustion chamber with an inlet port forprimary combustion air, apparatus for introducing into the combustionchamber primary fuel for combustion with the primary air, an exhaustport for combustion products, and an exhaust system for exhausting thecombustion products to atmosphere, the method including introducing intothe exhaust system secondary air, mechanically acting upon the secondaryair and products of combustion in the exhaust system in the presence ofa catalyst, to produce a reformed fuel, and introducing the reformedfuel into the combustion chamber for combustion with primary fuel andprimary air.
 2. A method according to claim 1 wherein the reformed fuelis introduced in the combustion chamber via the exhaust port.
 3. Amethod according to claim 1 wherein the combustion apparatus is aninternal combustion engine and secondary air is introduced into theexhaust system via an exhaust aspirator which draws air into the exhaustsystem during low pressure or partial vacuum conditions occurring duringthe cycle of pressure changes which occur in the exhaust system duringnormal operation of the engine.
 4. A method according to claim 3 whereinthe exhaust aspirator is tuned to draw air into the exhaust system andmechanically to act upon the secondary air and products of combustion bymeans of pressure pulses, in a manner to optimize reformed fuelproduction.
 5. A method according to claim 3 wherein the aspiratorincludes a valve with a spring biased valve member, the force of thespring acting to urge the valve member into engagement with a valve seatto close the valve, and the force of the spring being overcome whensufficiently low pressure is developed in the exhaust system, to allowthe secondary air to be drawn in through the valve and the aspiratorbeing tuned by adjusting the spring pressure so that the valve respondsto a desired low pressure or partial vacuum at an appropriate timeduring the engine cycle, and in a manner to produce strong pressurepulses in the exhaust system adequate mechanically to act upon thecombustion products and secondary air present in the exhaust system inthe presence of the catalyst, to produce reformed fuel.
 6. A methodaccording to claim 1 wherein the reformed fuel includes one or both ofmethanol and hydrogen gas.
 7. A method according to claim 3 wherein thecatalyst is provided by materials from which the aspirator is at leastpartly made.
 8. A method according to claim 1 wherein the combustionapparatus is a reciprocating piston engine and the reformed fuel isintroduced into the or each combustion chamber of the engine as a resultof a partial vacuum being established at the exhaust port at the end ofan exhaust stroke of a piston thereof as the piston commences its nextinduction stroke, before the exhaust port is completely closed by one ofan exhaust outlet valve and the piston.
 9. A method according to claim 1wherein the combustion apparatus has a plurality of combustion chamberseach having an exhaust port, the exhaust ports each opening to anexhaust manifold, where the apparatus for introducing secondary air intothe exhaust system is located.
 10. A method according to claim 1 whereinthe method includes introducing reformed fuel obtained by mechanicallyacting upon drawn in secondary air and products of combustion in theexhaust system, into an inlet manifold from where air is introduced intothe combustion chamber for combustion with the primary fuel.
 11. Amethod according to claim 1 wherein the method of the invention includesintroducing into the combustion chamber of the apparatus, a vaporizedsecondary hydrocarbon based high calorific value fuel, obtained by oneof heating a mineral oil electrically and by heat exchange with hotexhaust gases produced by the apparatus to vaporize the oil.
 12. Amethod according to claim 11 and wherein the combustion apparatus is aspark ignition engine and the primary fuel is one of induced andinjected into the combustion chamber together with the vaporizedsecondary hydrocarbon based high calorific value fuel.
 13. A methodaccording to claim 11 wherein the combustion apparatus is an engine isof the kind in which the primary fuel is introduced by an injectionapparatus, and vaporized secondary hydrocarbon based high calorificvalue fuel is introduced with the induced air.
 14. A method of adaptinga combustion apparatus having at least one combustion chamber an inletport for primary combustion air, an apparatus for introducing into thecombustion chamber primary fuel for combustion with the primary air, anexhaust port for combustion products, and an exhaust system forexhausting the combustion products to atmosphere for operation by amethod including introducing into the exhaust system secondary air,mechanically acting upon the secondary air and products of combustion inthe exhaust system in the presence of a catalyst, to produce a reformedfuel, and introducing the reformed fuel into the combustion chamber forcombustion with primary fuel and primary air, the method of adaptationincluding providing the combustion apparatus with an apparatus tointroduce into the exhaust system secondary air, providing a devicemechanically to act upon the secondary air and products of combustion inthe exhaust system in the presence of a catalyst, to produce thereformed fuel, and apparatus to introduce the secondary fuel into thecombustion chamber via the exhaust port for combustion with primary fueland primary air.
 15. A method according to claim 14 wherein thecombustion apparatus is an engine of a vehicle, the vehicle engine ofwhich is to be adapted includes a catalytic converter already and anengine management system thereof is provided with an input from a sensorassociated with the catalytic converter which affects engine control,the method including one of disabling the sensor of the catalyticconverter and re-programming the engine management system.